Complete each sentence using the correct ending from those listed below.

a. A catalyst is

b. Chemical reactions can only happen when

c. Concentration, surface area and temperature can all affect

d. An enzyme is

e. The activation energy is

Choose endings from:
◆ the minimum amount of energy that the particles must have to react.
◆ the rate of a chemical reaction.
◆ reacting particles collide with one another.
◆ a substance that can speed up the rate of a chemical reaction.
◆ a biological catalyst.